1. Technical Field
The disclosure relates to a measuring apparatus, and more particularly, to an apparatus of measuring a workpiece.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional apparatus 90 of measuring a workpiece includes a horizontal rail 91 and a measuring member 92 that is movable on the horizontal rail 91. The measuring member 92 has a threaded rail 921, an upper driving portion 922, a lower driving portion 923, an upper arm 924 and a lower arm 925. The threaded rail 921 is divided into an upper threaded section 921A and a lower threaded section 921B, wherein the upper threaded section 921A has a thread direction reverse to that of the lower threaded section 921B. The upper driving portion 922 is movably positioned at the upper threaded section 921A and the lower driving portion 923 is movably positioned at the lower threaded section 921B. The upper arm 924 is positioned at the upper driving portion 922 and the lower arm 925 is positioned at the lower driving portion 923. When the upper driving portion 922 moves at the threaded rail 921, it will cause the threaded rail 921 to rotate accordingly. This way the upper arm 924 and lower arm 925 will move simultaneously in reverse directions. Similarly, the movement of the lower driving portion 923 at the threaded rail 921 may also cause the upper arm 924 and lower arm 925 to move simultaneously in reverse directions.
However, the conventional apparatus 90 of measuring a workpiece has the drawbacks as follows:                (1) Since the upper arm 924 and lower arm 925 are driven to move simultaneously in reverse directions, the run-out of a workpiece 70 toward either of the upper arm 924 and lower arm 925 will cause the upper arm 924 and lower arm 925 to move away from each other. This will hinder the run-out measurement of the workpiece 70.        (2) Since the upper arm 924 and lower arm 925 are driven to move simultaneously, the connection between the upper threaded section 921A and lower threaded section 921B is required to be positioned corresponding to the axis of the workpiece 70 in order to take an accurate measurement.        (3) Since the upper arm 924 and lower arm 925 are driven to move simultaneously, it is difficult to determine whether the eccentricity of the workpiece of a roller originally comes from the production of the roller, a deformation of the roller neck or a grinding process of the roller.        
Accordingly, there exists a need to provide a solution to solve the aforesaid problems.